1. Field of the Invention
This invention relates to a method for imaging the surrounding for a vehicle. The invention also relates to a cruise control system in which a control unit controls driving parameters of the vehicle.
2. Related Art
The use of image sensors, such as cameras, is proliferating in vehicles. By way of example, cameras are used in park control systems where the image sensor images the back of the vehicle to detect obstacles and to show the surrounding of the back of the vehicle to the driver. Additionally, cruise control systems have been developed in which the front of the vehicle is investigated to look for approaching objects, such as other vehicles. In these cruise control systems, the relative distance between the object moving in front of the vehicle and the vehicle must be determined. When it is determined that an object is getting too close to the vehicle, the driver may be informed or the cruise control system may even actively control the motor by decelerating or accelerating the vehicle. Conventional image sensors, such as CCD or CMOS image sensors, measure the intensity of the scene, but lacks depth information. Conventionally, three dimensional (“3D”) information can be obtained by using two, two dimensional (“2D”) image sensors such as CCD cameras and mathematics.
Additionally, 3D image sensors have been developed, these sensors overcoming drawbacks faced by commercially available 2D sensors. Such 3D optical measurements deliver the absolute 3D geometry of objects that are largely independent of the objects' surface reflectivity, the distance of the objects from the sensor and the illumination conditions. One example of a 3D camera is a PMD (photonic mixer device) sensor. The PMD sensor measures the distance by emitting a light signal and by calculating the time of flight of the reflected light signal. These 3D image sensors are semiconductor elements. A 3D image can be obtained by positioning several 3D sensor elements in a matrix allowing the measurement of different pixels and therefore the measurement of a complete image.
When the signal of an image sensor is to be used in systems assisting the driver by detecting objects approaching the vehicle or by tracking the vehicle in front of the image sensor, the image data has to be updated at a high rate. When the image signal should be used on highways with high velocity, frame rates (images per time) such as 100 frames/second are necessary. When a complete 2D image is calculated 100 times a second, high computing power is needed to process the images and to detect the relevant information in the images.
Accordingly, a need exists to provide a method and system for imaging the surrounding of a vehicle in which the computing power can be reduced and in which nevertheless the object detection is assured.